Breaking shear pins on my mower

   / Breaking shear pins on my mower #1  

robsym240

Member
Joined
May 10, 2013
Messages
47
Location
columbia illinois
Tractor
yanmar ym240
My YM240 came with a John Deere 260 5ft. Finish Mower that does a great job but every time I press on the clutch while the mower is running I have to throttle down and restart, slowly letting out the clutch or it snaps the shear pin (a nut, lock washer n bolt) and I have to shut it down and put another one in. It's getting better as I get used to using the tractor, last cut I only went through 3 and I'm getting pretty fast at installing them, but it's still a pain, any suggestions? I saw this over running clutch that Hoye offers could that help? Yanmar over running clutches
 
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   / Breaking shear pins on my mower #2  
I don't think an over run clutch will do anything to prevent breaking a shear bolt. I've only broken 1 on my brush cutter in 7-8 yrs and that;s when I hit a stump. I use bolts that I buy from HD or Lowes for shear bolts
 
   / Breaking shear pins on my mower #3  
Breaking just on wind up, correct ?

What grade shear bolts are you using and what grade does the unit call for ?

I think the clutch you would be looking for is a 'slip' clutch.
 
   / Breaking shear pins on my mower
  • Thread Starter
#4  
I don't think an over run clutch will do anything to prevent breaking a shear bolt. I've only broken 1 on my brush cutter in 7-8 yrs and that;s when I hit a stump. I use bolts that I buy from HD or Lowes for shear bolts
Yeah, it's always user error, I'm in a turn and want to slow down but pop the clutch too fast by accident or forget the mower is running and use the clutch wrong, beginner mistakes. I get grade 8 bolts at Rural King pretty cheap, time to go get a few dozen! :)
 
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   / Breaking shear pins on my mower #5  
You already have an overrun clutch inside the YM240 transmission. This is one of the few differences from the similar YM2000. It sounds like a giant bicycle coaster ratchet. Its purpose is so the implement can't push you forward after you declutch. That Hoye diagram explains it well.

If you are breaking factory-grade shear pins it sounds like the tractor and mower aren't well matched. As Willl already said a slip clutch, carefully set up, should prevent overloading the mower.
 
   / Breaking shear pins on my mower
  • Thread Starter
#6  
Breaking just on wind up, correct ?

What grade shear bolts are you using and what grade does the unit call for ?

I think the clutch you would be looking for is a 'slip' clutch.

It calls for grade 9 but even the JD dealer only had grade 5, I found grade 8. Thanks, I'll read up on a slip clutch.
 
   / Breaking shear pins on my mower #7  
It calls for grade 9 but even the JD dealer only had grade 5, I found grade 8. Thanks, I'll read up on a slip clutch.


On the bolts I've seen and used. the dots on the head of the bolt indicates the grade. The shear bolts I use don't even have dots. So, their probably way softer bolts than you are using.
 
   / Breaking shear pins on my mower #8  
I been using a 5Ft. JD. FM for over 5yrs with a Ym2000 and never had a problem. I just pulled out the owners manual from curiousity to see if there is Shear Pin. Nope? I do Have one on a new to me Bush Hog thats located were the Dr.shaft and Gear Box connect. That is a Large Bolt. I would think it to be rather difficult to break that with a FM. Something don't seem right?
 

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   / Breaking shear pins on my mower #9  
I don't recall reading if your tractor has a live PTO ? and or is single or multiple speeds? If your tractor is 1 speed PTO doesn't it put it @ 1to1 ratio,
meaning the mower will cut at the engine speed/rpm's , apparently when applying the clutch causing the blades to free spin and then releasing it back into gear the engine speed is not matching the speed of the mower there for shearing the bolt, I would guess that it needs an over ride clutch, although if is live PTO it shouldn't need one, I would try to barrow one and see if it helps,
another thought... has the belt been replaced? Is there a belt tensioner free to move on the mower? or is it pulled tight against the belt? can it be adjust to allow the belt to slip some?
The belt on the mower I had was not stretch tight, actually was loose but not so it would come off,
 
   / Breaking shear pins on my mower #10  
a friend of mine had an old JD finish mower about that size, it was yellow though and old. He said that it kept breaking shear bolts, he finially went to grade 8 cause the 5's just snapped the first time a load was put on it. He was useing a jd 1020 so its more powerfull but he still said the 5's with the slightest amount of grass they broke. He said with the 8's they still broke every so often so i guess even there not to hard, and i see now if the manual calls for 9 that would make sense!
 
 
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